U0198 on 2017-2019 GMC Sierra 1500: Lost Communication with Telematics Module Fixes

What's Unique About the 2017-2019 Gmc SIERRA 1500

For this generation of GMC Sierra and its platform mates (like the Silverado, Tahoe, and Yukon), the Serial Data Gateway Module (SDGM) is a known weak point. GM has issued multiple Technical Service Bulletins (like #PIT5586G and its successor #20-NA-212) that link code U0198 to either internal software freezes ('logic lock') within the SDGM or physical problems with its electrical connectors. Unlike other vehicles where U0198 might point directly to a bad OnStar module, on the Sierra, the diagnostic path almost always starts at the gateway module that acts as the vehicle's network router.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: This range covers the end of the third generation (K2XX, 2017-2018) and the start of the fourth generation (T1XX, 2019). While the architecture is different, the U0198 code and its relation to the Serial Data Gateway Module and Telematic Control Module are common issues on both platforms. TSB 20-NA-212 was updated to include 2017, 2018, and clarified 2019 models, showing the issue's prevalence.

Symptoms You May Notice

• OnStar system inoperative (red light on mirror)
• GPS/Navigation shows incorrect location, fails to load, or displays a red circle with a slash through it.
• GMC mobile app features fail to work (remote start, lock/unlock).
• In-vehicle Wi-Fi hotspot does not work.
• "Service Telematics System" message on the driver information center.
• Check Engine Light may be on.
• Phantom battery drain may occur in some cases.

Most Likely Causes

1. Serial Data Gateway Module (SDGM) Logic Lock or Connector Issue 🔴 High Probability This is a well-documented issue covered by GM Technical Service Bulletins #PIT5586G and #20-NA-212. The module can freeze due to a software error, or the main X1 (black) and X2 (gray) connectors can develop poor pin tension or corrosion.
   How to confirm: A professional scan tool will show a loss of communication with multiple modules. Visually inspect the black and gray connectors on the SDGM, located under the driver's side dash, for any backed-out or loose terminals. A temporary fix after a battery disconnect also points to a logic lock.
   Typical fix: First, attempt a module reprogram at a dealership, which can fix a software 'logic lock' as per TSB 20-NA-212. If that fails, the connector terminals may need to be repaired (TSB specifies terminated lead P/N 84619127) or the connectors simply need to be unplugged and securely reseated.
   Est. part cost: $0 - $250
2. Failed Telematic Control Module (OnStar Module) 🟡 Medium Probability These modules have a high failure rate on GM trucks and SUVs. Forum discussions and technician comments confirm they are replaced very frequently, and parts can sometimes be on backorder.
   How to confirm: If the SDGM has been reprogrammed and its connections are verified to be good, the Telematic Control Module is the next likely point of failure. Diagnosis involves confirming it has proper power and ground at its connector before condemning the module.
   Typical fix: Replacement of the Telematic Control Module. The new module must be programmed to the vehicle by a dealer or a qualified shop. OnStar may also need to provision the new module on their end.
   Est. part cost: $250 - $450
3. Weak or Failing Vehicle Battery ⚪ Low Probability Modern vehicles are highly sensitive to system voltage. A weak battery can cause random, unpredictable communication errors between modules as they power up, especially during engine cranking.
   How to confirm: Test the battery's voltage and health with a multimeter or a dedicated battery tester. A healthy, fully charged battery should read approximately 12.6 volts with the engine off.
   Typical fix: Recharge or replace the vehicle's 12V battery.
   Est. part cost: $150 - $350

Rare But Worth Checking

• Poor Ground Connection (G218): A loose or corroded ground at location G218, under the driver's side dash near the A-pillar, can cause widespread communication issues. TSB PIT5405C addresses various electrical issues stemming from this ground, which can get insulation trapped under it. Several YouTube videos show owners fixing this ground to resolve strange electrical problems.
• Damaged CAN Bus Wiring: The wiring between the Telematic Control Module and the Serial Data Gateway Module can be damaged, shorted, or corroded, leading to a loss of communication. This is less common than module or connector issues but can happen, especially after collision repair or aftermarket accessory installation.

Diagnosis Steps

1. Check the vehicle's battery to ensure it is fully charged and healthy. Low voltage can cause numerous communication codes.
2. Scan for all Diagnostic Trouble Codes (DTCs) using a professional-grade scan tool. Note all 'U' codes present. A flood of U-codes points to the SDGM.
3. Follow GM TSB #20-NA-212. The first step recommended by the manufacturer is to attempt to reprogram the Serial Data Gateway Module (SDGM). This requires a trip to a dealer or equipped independent shop.
4. If reprogramming does not work, locate the SDGM under the driver's side dash, to the left of the brake pedal.
5. Disconnect the battery. Carefully inspect the black (X1) and gray (X2) connectors at the SDGM for any bent, loose, or corroded terminals. Often, simply unplugging and firmly reconnecting them can restore communication.
6. Inspect ground G218 under the driver's side dash near the A-pillar for looseness or corrosion.
7. If connectors and grounds are okay, check the power and ground circuits for the Telematic Control Module itself. On the K2XX platform (2017-2018), it's typically located behind the glovebox area.
8. If all wiring, connectors, and the SDGM check out, the Telematic Control Module is the most likely failed component and should be replaced and programmed.

Parts You'll Likely Need

• Serial Data Gateway Module (SDGM) (OEM #13599318 (supersedes 13509768, 13524297, 13524298, 13599317)) — This module is the central router for network communications and is a known failure point, either requiring a software update or replacement due to internal faults or connector issues.
  Trusted brands: ACDelco (GM Genuine Parts)
  OEM price range: $150-$400
  Aftermarket price range: $100-$300
• Telematic Control Module (OnStar Module) (OEM #84293872 (for 2018 models, check specific VIN for others like 84644344 for 2019)) — This module has a high failure rate and is often the cause if the SDGM and its wiring are confirmed to be good.
  Trusted brands: ACDelco (GM Genuine Parts)
  OEM price range: $250-$450
  Aftermarket price range: $200-$350

Related Codes That Often Appear With This One

• U0155 — Lost Communication with Instrument Panel Cluster. This often appears with U0198 when the SDGM is the root cause, as it disrupts communication across multiple networks.
• U0140 — Lost Communication with Body Control Module. Another common code when the SDGM has a fault, indicating a wider network problem.
• U1962 — Unable to Authenticate Serial Data Message. This code can appear with U0198, indicating a security handshake failure on the network, often pointing to the same faulty module or connection.

Technical Service Bulletins (TSBs) & Recalls

• PIT5586G: Instructs dealers to check for logic lock of the Serial Data Gateway Module or for issues with its X1 and X2 connectors for a list of U-codes including U0198. This TSB has been superseded.
• 20-NA-212: Supersedes PIT5586G, providing a more detailed diagnostic path for SDGM issues. It explicitly states to reprogram the SDGM first. If the issue persists, the TSB then directs technicians to inspect the X1/X2 connector terminals for being bent, backed out, or having loose tension.

Platform-Specific Known Issues

• GM Technical Service Bulletin #PIT5586G and its successor #20-NA-212 specifically address U0198, pointing to either a software 'logic lock' in the Serial Data Gateway Module or a physical problem with its X1/X2 connectors.
• TSB PIT5405C details various electrical gremlins that can be caused by a poor G218 ground connection, which can contribute to or mimic the U0198 fault.

Mechanic-Grade Diagnostic Values

• CAN Bus Network Resistance — expected: Approximately 60 Ω. Failure: A reading of 120 Ω indicates an open circuit or an offline terminating resistor. A reading significantly below 60 Ω suggests a short circuit.
• Ground Circuit Resistance — expected: Less than 0.2 Ω. Failure: A reading higher than 0.2 Ω indicates a corroded, loose, or otherwise high-resistance ground connection that requires cleaning or repair.
• CAN Bus Line Voltage Swing — expected: A swing between 2.5V and 3.5V on CAN High and 2.5V and 2.0V on CAN Low.. Failure: A lack of voltage swing or voltage stuck high/low indicates a faulty transceiver or a short/open on the line.

Hidden / Shadow Codes Worth Checking

• U1962: Unable to Authenticate Serial Data Message. This code indicates a failure in the security handshake between modules on the CAN bus. (see via A professional scan tool that can read codes from all vehicle modules. It often appears alongside U0198 when the Telematics or Gateway module fails.)

Scan Tool Commands That Help

• GM GDS2 / Techline Connect: Serial Data Gateway Module (SDGM) Reprogramming — This is the first step recommended by GM TSB #20-NA-212 to fix a suspected software 'logic lock' in the SDGM, which can cause U0198 and other communication codes.
• GM GDS2: Module Status / DTC Display — Used as the initial step to see which modules on the network are reporting 'No Communication'. If many modules are offline, it points to a gateway (SDGM) or network-wide problem.
• Professional Scan Tool: CAN Bus Monitor — To view live data traffic on the network. The absence of data frames from the Telematics module while other modules are transmitting confirms it is isolated.

Wiring & Ground Locations

• Serial Data Gateway Module (SDGM) — In the driver's side footwell, located up and to the left of the brake pedal, near the BCM. It is a small box with one gray and one black connector (X1 and X2).. This is the central network hub. TSBs point directly to poor connections at its X1/X2 connectors as a primary cause of U0198.
• SDGM Black Connector (X1 or X2) - CAN Bus Pins — On the SDGM module under the driver's dash.. An aftermarket installation guide identifies Pin 5 (Blue wire) and Pin 6 (White wire) on the black connector as specific CAN bus lines. These are the exact pins to test for continuity and signal integrity when diagnosing a communication failure with the Telematics module.
• Telematic Control Module (OnStar) — On the 2017-2018 K2XX platform, it is typically located behind the glove box. Its location may differ on the 2019 T1XX platform and should be professionally verified.. This is the module that has lost communication. A technician must access its connector to test for power, ground, and CAN signals before condemning the module.
• Ground G218 — Under the driver's side dash, near the A-pillar. It is a ground stud on the body.. This is a major ground point for several modules, including the BCM. A poor connection here (often from trapped insulation) can cause widespread, intermittent network instability and trigger U0198.

Real Owner Repair Stories

• OnStar Community Forum / Reddit r/gmcsierra (2019+ GMC Sierra / Chevy Silverado) — GPS shows incorrect location, red light on OnStar mirror, GMC app fails to connect, "Service Telematics System" message, Check Engine Light on.
  ❌ Tried (didn't work) Disconnecting the battery for a short period., Attempting to reset the infotainment system through the screen menus.
  ✅ What actually fixed it The common resolution path involves a dealer visit. The dealer diagnoses a failed Telematics Control Module (OnStar module) and quotes a replacement. Owners report costs ranging from $750 to over $1,000, especially if the vehicle is just out of the 36,000-mile bumper-to-bumper warranty. A frequent complaint is that the replacement module is on national backorder, sometimes for weeks or months, leaving the owner without connected services.

OEM Part Supersession History

• 13509768, 13524297, 13524298, 13599317 → 13599318 — Standard part revision and consolidation by GM.
  Heads up: The newest part number should be used, but programming is always required for the module to function in the vehicle.

Model Year Variations Within This Range

• 2017-2018 vs 2019: The 2017-2018 models are built on the K2XX platform, while the 2019 model is the first year of the new T1XX platform. While the U0198 fault related to the SDGM is common to both, the physical location of the Telematics Control Module may be different. On K2XX trucks, it is commonly found behind the glove box. On the newer T1XX platform, module locations were changed, and professional verification (e.g., service information) is needed to pinpoint the Telematics module's exact location.